They occupy the same majestic building on Capitol Hill, but there are times -- like now -- when the House and Senate seem to sit on different planets.

Rank-and-file GOP lawmakers in both houses seethed over their party's poor showing in the Nov. 3 elections, accusing their leaders of losing the cutting edge that helped the GOP win control of Congress only four years ago. Senators, no less than House members, complained that the leaders have no agenda, no message and no hope for keeping control of Congress unless drastic changes are made.

But their resulting actions could not have been more different.

In the House, an insurrection in Republican ranks forced Speaker Newt Gingrich (R-Ga.) to step down and triggered efforts to unseat other GOP leaders in party elections scheduled for today. But Senate Majority Leader Trent Lott (R-Miss.) appears to have escaped challenge, and there is only one threatened contest for a second-tier leadership post when the Senate chooses its new leaders Dec. 1: a possible bid by freshman Sen. Chuck Hagel (Neb.) to unseat Sen. Mitch McConnell (Ky.) as chairman of the GOP's senatorial campaign committee.

Lott's good fortune is rooted in both the distinct culture of the Senate, where any change is viewed warily, and in the fact he isn't Gingrich. The outgoing House speaker had become a lightning rod for dissension within the party and his departure eased some of the pressure for change in the Senate, according to key GOP senators. Lott was less visible and consequently less vulnerable.

"Fairly or unfairly, Newt was demonized as the face of the Republican Party in a way that Trent was not," said Sen. Robert F. Bennett (R-Utah). "Therefore, getting Trent's scalp didn't mean anything."

"Gingrich and [House Majority Leader Richard K.] Armey are seen as liabilities as public officials," said Thomas E. Mann, director of governmental relations at the Brookings Institution. "Lott hasn't helped any, but he's not been visible enough to be a serious national political liability to the party."

Unlike Gingrich, who faced formidable opposition from House Appropriations Committee Bob Livingston (R-La.) for another term as speaker, Lott was home free so long as Sen. Don Nickles (R-Okla.), the assistant majority leader, refrained from opposing him.

Nickles, whose relations with Lott are not particularly close, was under some pressure from fellow conservatives to challenge Lott. But, according to associates, Nickles was reluctant to do so unless he was virtually drafted by his colleagues -- which they were not willing to do. Hagel hinted he might challenge Lott but did not do so. With no other prospective challengers waiting in the wings, any hint of trouble at the top vanished when Nickles announced last week that he was running again for the No. 2 spot.

In explaining the relative stability in their leadership, senators also cited the fundamental differences between the House and Senate that date back to the founding of the republic, when the Senate was created as a brake on popular passions championed by the House.

With two-year terms, "the House lives with minute-to-minute pressures and acts accordingly," Hagel observed. With six-year terms, senators "take a longer view of things -- and that goes for its leadership too," he added. Hagel plans to decide by week's end whether to run against McConnell.

Because of the filibuster and other rules and traditions that vest enormous power in individual senators, "you're reluctant to make enemies in an institution where one guy can stop anything," observed Sen. James M. Inhofe (R-Okla.), a former House member.

In the House, leadership challenges are also encouraged because of the large number of members -- 435 instead of 100 -- and the fact that many members have voluntarily accepted to limit the amount of time they will serve.

"When you have that many people with that much ambition, with a fairly short timetable in which to accomplish things, I think they feel greater need to act to accelerate their chances for upward mobility," said Minority Leader Thomas A. Daschle (D-S.D.), another House graduate.

Even without these differences, Lott and other top Senate GOP leaders may have been in less trouble than their House counterparts.

For one thing, Republicans, who had been hoping to gain seats in both houses in the elections, lost five seats in the House but held their own in the Senate. The Republicans' margin of control is also proportionately greater in the Senate than the House: 55 to 45 as opposed to 223 to 211.

For the Senate, it was a "status quo election" and less of a cause for rebellion, Mann said.

Even so, Lott faces strong new pressures to sharpen the Senate Republicans' focus. A group of relatively junior senators recently fired off letters calling for an early meeting of the Senate GOP conference to start work on an agenda for next year, including tax cuts and budget process reforms, and for the Senate to start work in early January, rather than waiting until after the president's State of the Union message several weeks later.

"If Republicans are going to continue to hold the majority, we must articulate a clear, concise message to the American people," they said.